Ultrasonic, flow measuring devices are widely applied in process and automation technology. They permit simple determination of volume flow and/or mass flow in a pipeline. Known ultrasonic, flow measuring devices work frequently according to the travel-time difference principle. In the case of the travel-time difference principle, the different travel times of ultrasonic waves, especially ultrasonic pulses, so-called bursts, are evaluated as a function of flow direction of the liquid. For this, ultrasonic pulses are sent at a certain angle to the pipe axis both with, as well as also counter to, the flow. From the travel-time difference, the flow velocity, and therewith, in the case of the known diameter of the pipeline section, the volume flow rate, can be determined.
The ultrasonic waves are produced, respectively received, with the assistance of so-called ultrasonic transducers. In the case of a widely used manner of construction of clamp-on, ultrasonic, flow measuring devices, the ultrasonic transducers are pressed externally on the wall of a pipe. A great advantage of clamp-on, ultrasonic, flow measuring systems is that they do not contact the measured medium and are placed on an already existing pipeline.
The ultrasonic transducers are, normally, each composed of an electromechanical transducer element, e.g. a piezoelectric element, and a coupling element, the so-called coupling wedge. In the case of clamp-on-systems, the ultrasonic waves are produced in the electromechanical transducer element as acoustic signals and led via the coupling element to the pipe wall and from there into the fluid, i.e. the measured medium.
In the case of clamp-on, ultrasonic, flow measuring devices, depending on the embodiment of the measuring point, a complex measurement error can result, which depends on different influencing factors.